1. Field
The present invention relates to a power supply device, an information processing apparatus, and a power control method. In particular, the present invention relates to a power supply device that controls a voltage or the like under the control of a pulse width, and an information processing apparatus including the power supply device, and a power control method.
2. Description of the Related Art
A power supply device, such as a power supply device for DC/DC conversion, conventionally uses a technology for controlling an output voltage or output power under the control of a pulse width or a duty ratio in many cases.
In the power supply device for DC/DC conversion, DC power is input to a switching element, such as an FET, the input power is switched with a pulse signal having a predetermined duty ratio, the power is thereafter smoothed, and DC power with a desired voltage is output. Since an output voltage can be easily controlled by the duty ratio of the pulse signal applied to the switching element, the power supply device for DC/DC conversion is used as a power supply of an information processing apparatus in many cases.
Further, in power supply devices for DC/DC conversion, even when a load is changed, the duty ratio (or pulse width) of the pulse signal is controlled in real time to continuously keep the output voltage to be constant.
The power supply device for DC/DC conversion having a control function with the duty ratio (or pulse width) requires high control-responsiveness to the change in load.
For example, Jpn Pat Publication No. 10-2248 discloses a technology for realizing the high control-responsiveness under the control of the duty ratio of current with an electric load, and the technology relates to an energization control apparatus similar to the power supply device for DC/DC conversion.
Generally, the power supply device for DC/DC conversion for controlling the duty ratio or pulse width uses such a method that an output voltage is monitored, a new duty-ratio or pulse-width is calculated from the monitored output voltage, and the calculated pulse-period or pulse-width is set to a register in a predetermined pulse-generating circuit, the new pulse-signal is thus generated, and the output voltage is sequentially updated and controlled by switching DC power with the new pulse-signal.
With the conventional power supply device for DC/DC conversion, even if the new pulse-width or pulse-period is calculated, actually, a new pulse signal based on them can be generated in the next pulse-period or the pulse-period subsequent thereto.
Further, in order to calculate the new pulse-width or pulse-period from the monitored output voltage at the current pulse period and apply the calculated pulse period to a next one, calculating processing and setting processing to the register in the pulse generating circuit is necessary within the pulse period. When a processing speed is not sufficient, the pulse period is necessarily long.
As mentioned above, with the conventional technology, a response is delayed from the time for calculating the new pulse-width or duty-ratio on the basis of the change in voltage to the time for actually generating a pulse waveform having a new pulse-width or duty-ratio.
Jpn Pat Publication No. 10-2248 discloses a technology for updating the pulse width within the pulse period as much as possible in order to improve the above-mentioned responsive delay. Although the technology disclosed in Jpn Pat Publication No. 10-2248 is improved to some degree, as compared with the conventional technology, the new pulse-width is not realized without the responsive delay from a changing instruction of the pulse width. Further, in the case that the changing instruction of the pulse width is issued during an ON-pulse time, the new pulse-width cannot be realized until the next pulse-period.
On the other hand, the improvement in responsiveness of the power supply device for DC/DC conversion is increasingly demanded. The recent fast improvement in information-processing speed results not only in increase in consumption power of a CPU but also in increase in changing rate of consumption current varying depending on the operation of the CPU. In order to prevent the fall in power voltage due to the abrupt increase in consumption current, a large-scaled-capacitor needs to be provided for a peripheral power circuit of the CPU.